Brake systems in motor vehicles with automatic functions for supporting start-up, such as, for example, the independent release of the applied emergency brake or parking brake on starting up may cause comfort problems, in particular as the motor vehicle moves off from the stationary position, because the time for releasing the parking brake considerably influences the dynamics of the motor vehicle. In particular, in the case of electrical parking brakes, which are controlled by an electric motor transmission unit, the duration of the releasing process depends on the force used in the applied state or the distance of travel of the braking mechanics.
The time taken for release, for example, of an applied electrical parking brake with a mechanical brake system, is of the order of magnitude of approximately one second (1 s) or several 100 ms. However, in the case of a quick start-up maneuver it is possible for the time from the moment when the driver's intention to start up is signaled to the moment when the motor vehicle actually starts off to be considerably shorter.
The result of the difference in these times can be, that at the point in time of the expected movement of the motor vehicle such a high braking torque is still applied that the desired movement of the motor vehicle is restrained unnecessarily in this way and/or that there are unwanted comfort problems (such as, for example, “bucking” when starting up).
In the case of a few previous brake systems, these problems occur less frequently if the start-up functions are performed by an expensive, fast-acting hydraulic system (e.g. ESP) or the braking mechanisms used there do not have any major dynamic effects in this context.
For the purpose of preventing increased wear and tear of the brake system in a motor vehicle, it is also known from DE 198 14 657 A1 or DE 100 61 064 B4 that the braking force must be selected in accordance with the motor vehicle-specific characteristic values.